This invention relates to an integrated circuit including first and second capacitors which each comprise a pair of continuous plates which are spaced apart by a layer of dielectric material which has the same composition and thickness for the two capacitors, the area of a first plate of the first capacitor being equal to k times the area of the corresponding plate of the second capacitor, thereby determining the capacitance of the first capacitor to be substantially k times the capacitance of the second capacitor, where k is greater than unity, the total length of the boundary of said first plate being k times the total length of the boundary of said corresponding plate.
Such an integrated circuit is known from U.S. Pat. No. 4,210,950. Fabrication of such a circuit typically involves a processing sequence that includes various etching or similar steps. The length of the boundary of the first plate of the first capacitor is arranged to be k times the total length of the boundary of the corresponding plate of the second capacitor in order to reduce the sensitivity of the ratio between the capacitances to variations which inevitably occur in the capacitor fabrication process from circuit to circuit. In the known circuit the said corresponding plate of the second capacitor is substantially H-shaped and the shape of the said first plate of the first capacitor is effectively a plurality of H-shapes with their long sides butted together. Thus the periphery of each includes a series of 90.degree. and 270.degree. corners, and it is pointed out in U.S. Pat. No. 4,210,950 that, ideally, both the ratio of the number of 90.degree. corners in the first plate to the number of 90.degree. corners in the corresponding plate, and the ratio of the number of 270.degree. corners in the first plate to the number of 270.degree. corners in the corresponding plate, should also be equal to k (in fact in the known circuit to the integer portion of k, k consisting of an integer portion plus a small fraction). This is for the same reason that the total lengths of the boundaries are chosen to be in the ratio k, corner rounding effects, which are generally different in the case of 90.degree. corners and 270.degree. corners, also occurring in the etching steps used to fabricate the capacitors. However these ratios are inherently impossible to achieve simultaneously with the purely H-shaped corresponding plate and the first plate shaped purely as abutting H-shapes of the known circuit, because the H-shaped plate contains different numbers of 90.degree. and 270.degree. corners (eight and four respectively), whereas abutting an H-shape adds an equal number (four) of 90.degree. and 270.degree. corners. It is an object of the invention to enable this problem to be overcome.